The "Got Milk?" ads (and all their imitators) were ubiquitous at one point, but after running it for two decades, the dairy industry announced this year it has retired the campaign. The celebrities and the typeface will probably be its most remembered elements, but it's also interesting how the "Got Milk?" tagline targeted consumers at a specific stage in their thought process.
In the formation of the campaign, researchers were interviewing consumers, and one woman said, "The only time I even think about milk is when I run out of it," which prompted someone to write "Got Milk?" on a whiteboard.
This anecdote illustrates that whenever someone commits to any sort of purchase, there's a process going on in their mind that takes them from "Never heard of it" to "I don't really need it" to "I do need it" to "I'm going to buy that." Here's a rough diagram I drew up to illustrate this for milk:
"Got Milk?" doesn't speak to the product's taste or health benefits. It's simply about reminding people they may need something they normally like to have on hand. The tagline shows that while simple messages can be effective alone, they're best when they are targeted at strategic points in a buyer's thought process.